Unit Tests Worth It?

This interesting article about the value of unit tests has me thinking; what is the real value in unit tests?

I believe unit tests produce value to developers, but what about beyond that? Can we justify the cost beyond initial development to a business? When a project has reached maintenance, are unit tests actually worth maintaining?

Think of unit tests more as a debugging tool, not a metric to abide by. Code coverage might be a red herring... A project could have 100% code coverage and still have plenty of bugs and edge cases you never dreamed of. Also, just to point out, that tests themselves are code which could have bugs or missing features just as much as any other code.

I believe the end user cares about the features of the system. Developers should place more focus on integration tests as well as end-to-end tests for maximum feature coverage.